• We would like to remind our members that this is a privately owned, run and supported forum. You are here at the invitation and discretion of the owners. As such, rules and standards of conduct will be applied that help keep this forum functioning as the owners desire. These include, but are not limited to, removing content and even access to the forum.

    Please give yourself a refresher on the forum rules you agreed to follow when you signed up.

Axe-Fx III vs The real deal tube amp

tealtonerick

Inspired
I think that's not really the output impedance but the load impedance. The output impedance is a few milliohms IIRC.
Here's the datasheet of the PS170 power amp, you can check by yourself an you'll also find the circuit diagram and a few graphs:

https://icepower.dk/download/1633/

Thanks for that, I appreciate it. Yes, I understand that I was talking about the load impedance spec. But that's my question, considering that the output impedance spec is so low (as expected) and the output current is unlimited as per the data sheet, what is the problem say with a 2 Ohm load? Is it just a thermal issue?
 

DLC86

Fractal Fanatic
Thanks for that, I appreciate it. Yes, I understand that I was talking about the load impedance spec. But that's my question, considering that the output impedance spec is so low (as expected) and the output current is unlimited as per the data sheet, what is the problem say with a 2 Ohm load? Is it just a thermal issue?
Where did you read that the output current is unlimited? It can't be unlimited in real world, there are always a power supply and components that blow after a certain threshold.

EDIT: datasheet says that maximum current draw is 20A, so it's not unlimited

EDIT2:
Anyway, this should definitely answer your question

IMG_20200608_220747.jpg

Frequency response for 4 and 8 ohm loads is totally flat up to 20k, that would not happen with current feedback amps which, if I got it right, would behave like tube power amps in that the frequency response somewhat follows the speaker impedance curve.

Actually I think that happens cuz the output impedance of those amps (tube and class D current feedback) is much higher than solid state amps.
Tipically the optimal ratio between output impedance and load must be 1/100 or at least 1/10, if it's lower you get signal loss and alteration of the frequency response. That's true for pickups and amp's input stages or for amp's output and speaker.
 
Last edited:

tealtonerick

Inspired
Where did you read that the output current is unlimited? It can't be unlimited in real world, there are always a power supply and components that blow after a certain threshold.

EDIT: datasheet says that maximum current draw is 20A, so it's not unlimited

Yes, Iout is limited to 20A for protection, but I meant not limited otherwise. Shouldn't this still support a 2 Ohm load?
Where did you read that the output current is unlimited? It can't be unlimited in real world, there are always a power supply and components that blow after a certain threshold.

EDIT: datasheet says that maximum current draw is 20A, so it's not unlimited

EDIT2:
Anyway, this should definitely answer your question

View attachment 68604

Frequency response for 4 and 8 ohm loads is totally flat up to 20k, that would not happen with current feedback amps which, if I got it right, would behave like tube power amps in that the frequency response somewhat follows the speaker impedance curve.

Actually I think that happens cuz the output impedance of those amps (tube and class D current feedback) is much higher than solid state amps.
Tipically the optimal ratio between output impedance and load must be 1/100 or at least 1/10, if it's lower you get signal loss and alteration of the frequency response. That's true for pickups and amp's input stages or for amp's output and speaker.

OK, thanks. Then it sounds like the answer to my original question would be to use the FRFR output mode in an amp block for the PowerStage amps even though FRFR is obviously limited by the cabinet in that case. It also sounds like it won't hurt anything to at least try lower or even higher loads to hear what that sound likes. I am so conditioned to paying attention to proper transformer coupled loads in tube amps that I wanted to be sure that I understood what the potential limitations were. I don't have a great amount experience with these new class D beasts for guitar.
 

DLC86

Fractal Fanatic
Yes, Iout is limited to 20A for protection, but I meant not limited otherwise. Shouldn't this still support a 2 Ohm load?

Datasheet says minimu load is 3ohm, I wouldn't go lower than that for whatever reason that's stated.

Ok, thanks. Then it sounds like the answer to my original question would be to use the FRFR output mode in an amp block for the PowerStage amps even though FRFR is obviously limited by the cabinet in that case. It also sounds like it won't hurt anything to at least try lower or even higher loads to hear what that sound likes. I am so conditioned to paying attention to proper transformer coupled loads in tube amps that I wanted to be sure that I understood what the potential limitations were. I don't have a great amount experience with these new class D beasts for guitar.
Nope, the "right" setting for the powerstage is SS PA + Cab.
Anyway the difference between those two settings is subtle if you don't use a lot of speaker compression, I actually prefer ss + cab even when playing thru FRFR speakers.

Regarding the load, I don't think that will make any hearable difference either with that power amp.. or at least so says the graph above
 

tealtonerick

Inspired
Datasheet says minimu load is 3ohm, I wouldn't go lower than that for whatever reason that's stated.


Nope, the "right" setting for the powerstage is SS PA + Cab.
Anyway the difference between those two settings is subtle if you don't use a lot of speaker compression, I actually prefer ss + cab even when playing thru FRFR speakers.

Regarding the load, I don't think that will make any hearable difference either with that power amp.. or at least so says the graph above

Oh yes, thanks. I don't know why I said that. I flipped the polarity of the note in my mind. I will give the SS mode a try!
 

strabes

Member
I spent a few hours A/B between a new Mesa Boogie Tripe Crown TC-100 amp head going through a Mesa Boogie 2x12 cabinet against the Axe-FX III going through two new XiTone GRFR active cabinets.

In your comparison, the following variables are changing simultaneously between the two setups: amp, cab, speakers, mic, mic placement, and monitoring paradigm. When you run direct with a modeler using close-mic'd IRs, you're recreating the signal from a mic on a guitar cab in another room, monitored through whatever speakers you're using. It's a much different sound/feel than a live guitar cab in the room with you. Even a recording of your actual amp played back through those FRFR speakers will sound different than what you heard from the real cab in the room with you when you were playing it. So it's silly to blame the amp modeler for the difference in sound when it's almost entirely due to all of the variables I mentioned, most importantly the monitoring paradigm.

A proper apples-to-apples A/B test of the amp modeling would be: record some dry guitar in your DAW, reamp it through the real amp+cab+mic, and record the results. Then reamp the same dry guitar through the Axe-FX III amp model into a high quality solid state power amp and the same cab+mic setup you used with the real amp. Compare the two recorded tones through your studio monitors. This way you're controlling for all of the variables I mentioned above, and only changing the "amp" portion. These are the tones the audience hears through the PA. When done correctly, the accuracy is shocking.

You could do a similar apples-to-apples test by running the real amp into a load box and the same IR setup you're using with the Axe.

If you don't want to buy a power amp or load box, the next best test would be to use your studio monitors to compare the reamp'd recorded audio from the mic on the real cab to the reamp'd recorded direct signal from the Axe using IRs. It's not a perfect test since the cab, speakers, mic, and mic placement would all be changing simultaneously in addition to the amp, but at least it would control for the monitoring paradigm, which is the most important factor here.
 
Last edited:

Raab90

Inspired
If you compare 'real amp + cab' against 'axe fx (amp->cab IR) + FRFR' then don't expect them to sound the same, as the latter is like listening to a recorded guitar from an album or something. They sound drastically different that way.

If you do 'amp + cab' against 'axe fx (just amp block) + cab', using the same cab, things change.

I have a few tube amps (including mesas) and two 4x12 mesa cabs that allow for bi-amp configurations. In my personal experience. when plugging the axe fx III + Matrix GT1000FX on one side, and a real tube amp in the other side pf the same cab, I can't tell the difference between them either by sound or feel. I do however have to tweak the amps a little, but not to make them sound "more real", but to adapt them to what my amps sound like. After that, I just save the settings and it's like having my amp inside the axe fx.
 

Raab90

Inspired
Thanks for the info, very helpful. Are you saying use the Axe III through a guitar cab? I tried that once, with the power amp, don't recall what it was called, that supposedly, was for doing this kind of set up. Sounded worse than the Axe III through the XiTones.If you are suggesting I run the Axe III through a guitar cabinet...what power amp do you like?

Remember to turn the cab block off
 

Raab90

Inspired
At the risk of bothering people by banging on about my setup I think I should share my experience as it may help the OP.

With 25 years of semi-pro playing and audio engineering under my belt I was in a not too dissimilar spot, it left me with very “educated ears” compared to some.

Missing the feeling and sonic nuances of a tube amp and speaker cabinet making their magic together was one of my concerns when I was in the midst of switching to the Fractal Axe-Fx III.

I had a panic point when I had the Axe-Fx setup through Yamaha HS8’s, all my traditional guitar cabs in storage or packed ready to be shipped and found something missing.

Like the OP the recorded sound was great, monitored sound through the HS8’s was great but something was missing when I wasn’t listening from a critical engineering perspective or from the perspective of the consumer listener and just as a guitar player.

I rolled the dice on what it was and had Zilla make two custom 1x12 guitar cabs with the Celestion F12-X200 speakers in them and ordered a Matrix GT1000FX power amp.

For me that scratched the itch and I haven’t thought twice since.

I happily sit in the room and feel the cabs musically light up, resonate and fill the space when I play and for me there is nothing missing anymore.

The bottom line is, it’s as close to a guitar speaker in a guitar cab as I could get that still allows for the magic of IR’s and the Matrix lets the power amp modelling shine.

Maybe that’s the direction you need to head in.

This is interesting. Is Zilla planning on selling those? I'll eventually get an FM3 bc I'm using an ENGL Ironball for gigging but now I'm starting to need effects and more sounds, and there's no way I'm carrying around my entire rack + a 4x12 or a 100 Watt head. Reducing the load from a lunch box + 2x12 to a liddo pedal + 1x12 sounds like a good bet to me
 

Raab90

Inspired
Yes, Iout is limited to 20A for protection, but I meant not limited otherwise. Shouldn't this still support a 2 Ohm load?


OK, thanks. Then it sounds like the answer to my original question would be to use the FRFR output mode in an amp block for the PowerStage amps even though FRFR is obviously limited by the cabinet in that case. It also sounds like it won't hurt anything to at least try lower or even higher loads to hear what that sound likes. I am so conditioned to paying attention to proper transformer coupled loads in tube amps that I wanted to be sure that I understood what the potential limitations were. I don't have a great amount experience with these new class D beasts for guitar.

An amp can't violate the laws of physics, and will always have an energy limitation. In this case the actual limit is 20A, and protection means the unit's gonna cut the power off around 20A because it's is limit, and you'll destroy it otherwise.

If those speakers were not designed to be driven by that poweramp, I'd suggest you read the speakers' manual for what's the current limit for each coil, and what's the maximum voltage since it could eventually short the windings and mess everything up. In anyother case, just make sure the speaker cab sure can handle the power output for a particular impedance match and that's it
 

stereotactic

Experienced
If I am interpreting the OP’s observation correctly, I have had a similar experience, though my comparisons between real amps and the Axe have been much less exact since my main amp for 30 years is a heavily modded JCM800. The closest Axe 3 high gain sounds to my amp all seem to be missing a certain high end shininess or glare compared to my real amp sound. But for me, it’s a clear cut trade off I’m willing to make. My JCM800 sounds amazing, but lugging it around with a big rack is just not practical anymore for reasons technical and physical. While I miss the shiny, wide, high end splatter of my JCM800, I sure do have a clearer, more detailed sound with the Axe. Especially when playing bigger chords with major and minor intervals, I can really hear every note and the sound is so consistent every day. That and the infinitely flexible signal chain routing and switching without any signal degradation, there’s just no going back to the refrigerator rack.

I don’t know if the OP and I are talking about the same phenomenon, but I look forward to the new firmware nonetheless. Each new firmware has been a step closer!
 

biggness

Power User
If I am interpreting the OP’s observation correctly, I have had a similar experience, though my comparisons between real amps and the Axe have been much less exact since my main amp for 30 years is a heavily modded JCM800. The closest Axe 3 high gain sounds to my amp all seem to be missing a certain high end shininess or glare compared to my real amp sound. But for me, it’s a clear cut trade off I’m willing to make. My JCM800 sounds amazing, but lugging it around with a big rack is just not practical anymore for reasons technical and physical. While I miss the shiny, wide, high end splatter of my JCM800, I sure do have a clearer, more detailed sound with the Axe. Especially when playing bigger chords with major and minor intervals, I can really hear every note and the sound is so consistent every day. That and the infinitely flexible signal chain routing and switching without any signal degradation, there’s just no going back to the refrigerator rack.

I don’t know if the OP and I are talking about the same phenomenon, but I look forward to the new firmware nonetheless. Each new firmware has been a step closer!

Care to share your main presets?

I also feel that the 3d-ness of the upper midrange to highs is not quite there yet.
 

vguerriero

New Member
On any given week, I'm ready to go 100% AxeFx III or 100% tube amp rigs (I have both)...not being a regular gigging musician (occasional get together with a band) or a recording guy, I just have the good fortune of satisfying my guitar playing at home.

Been a player for 40 years....always (nutty?) searching for great tones....grew up on EVH/80s but love most genres (not really into industrial/djent kinda stuff which SEEMS to be where a lot of modeling folks are).

My latest "settling in" is on using my AxeFx III through a SD Powerstage 700 (have also had the Matrix GT1000fx) into a Mesa 1x12 Widebody Closed Back (with C90 speaker)and a Mesa 1x12 Lonestar Open Back (with Fillmore 75W speaker) AND a Xitone active wedge. I use Austin Buddy's 1400 naked amps presets and balance the dry tones to my guitar cabs and the wet tones to the FRFR....sounds very full/3D. All that said, it's hardly anymore portable than a tube amp rig and I know that I'm only using a minuscule amount of the AxeFx capabilities....should I care about that?

Also, I've just generally found that I don't like the tones of many amps AND/OR many variants of an amp (Marshall...Friedman...Splawn...Diezel, etc.) have so much overlap the choices become crazy....

With all of above, I also have a Mesa Mark v 90W combo that I also will plug into the two cabs OR a Friedman Smallbox into a 2x12 Friedman cab and then I swear that's all I need....

Net is that in all scenarios, I've got so many options and can make all sound good, but always wonder, do I REALLY need to have all this STUFF? Maybe I should buy something like an Ox Top or Torpedo Captive X (new one...I've had the Torpedo Live as well as the Studio unit) with my tube amps and a delay/reverb unit (all I really use) : )
 

ZipGun68

Member
On any given week, I'm ready to go 100% AxeFx III or 100% tube amp rigs (I have both)...not being a regular gigging musician (occasional get together with a band) or a recording guy, I just have the good fortune of satisfying my guitar playing at home.

Been a player for 40 years....always (nutty?) searching for great tones....grew up on EVH/80s but love most genres (not really into industrial/djent kinda stuff which SEEMS to be where a lot of modeling folks are).

My latest "settling in" is on using my AxeFx III through a SD Powerstage 700 (have also had the Matrix GT1000fx) into a Mesa 1x12 Widebody Closed Back (with C90 speaker)and a Mesa 1x12 Lonestar Open Back (with Fillmore 75W speaker) AND a Xitone active wedge. I use Austin Buddy's 1400 naked amps presets and balance the dry tones to my guitar cabs and the wet tones to the FRFR....sounds very full/3D. All that said, it's hardly anymore portable than a tube amp rig and I know that I'm only using a minuscule amount of the AxeFx capabilities....should I care about that?

Also, I've just generally found that I don't like the tones of many amps AND/OR many variants of an amp (Marshall...Friedman...Splawn...Diezel, etc.) have so much overlap the choices become crazy....

With all of above, I also have a Mesa Mark v 90W combo that I also will plug into the two cabs OR a Friedman Smallbox into a 2x12 Friedman cab and then I swear that's all I need....

Net is that in all scenarios, I've got so many options and can make all sound good, but always wonder, do I REALLY need to have all this STUFF? Maybe I should buy something like an Ox Top or Torpedo Captive X (new one...I've had the Torpedo Live as well as the Studio unit) with my tube amps and a delay/reverb unit (all I really use) : )
Only you can make that choice. The AxeFX III is the ultimate tool to pursue your musical visions. It can be overwhelming to have so many options, but in the end that is exactly what sparks new ideas for a lot of musicicans. Just because you have a crescent wrench, doesn't mean you can't benefit from a elaborate socket set. In the end you should just make music how you feel most comfortable. There are no firm answers to your question.

Good luck,
 

OrganicZed

Experienced
On any given week, I'm ready to go 100% AxeFx III or 100% tube amp rigs (I have both)...not being a regular gigging musician (occasional get together with a band) or a recording guy, I just have the good fortune of satisfying my guitar playing at home.

Been a player for 40 years....always (nutty?) searching for great tones....grew up on EVH/80s but love most genres (not really into industrial/djent kinda stuff which SEEMS to be where a lot of modeling folks are).

My latest "settling in" is on using my AxeFx III through a SD Powerstage 700 (have also had the Matrix GT1000fx) into a Mesa 1x12 Widebody Closed Back (with C90 speaker)and a Mesa 1x12 Lonestar Open Back (with Fillmore 75W speaker) AND a Xitone active wedge. I use Austin Buddy's 1400 naked amps presets and balance the dry tones to my guitar cabs and the wet tones to the FRFR....sounds very full/3D. All that said, it's hardly anymore portable than a tube amp rig and I know that I'm only using a minuscule amount of the AxeFx capabilities....should I care about that?

Also, I've just generally found that I don't like the tones of many amps AND/OR many variants of an amp (Marshall...Friedman...Splawn...Diezel, etc.) have so much overlap the choices become crazy....

With all of above, I also have a Mesa Mark v 90W combo that I also will plug into the two cabs OR a Friedman Smallbox into a 2x12 Friedman cab and then I swear that's all I need....

Net is that in all scenarios, I've got so many options and can make all sound good, but always wonder, do I REALLY need to have all this STUFF? Maybe I should buy something like an Ox Top or Torpedo Captive X (new one...I've had the Torpedo Live as well as the Studio unit) with my tube amps and a delay/reverb unit (all I really use) : )

Cliff recommends the Suhr or the Fractal LB-2 loadboxes because they have a more speaker like impedance curve to the load. The Torpedo load boxes are not very similar to the load of a real speaker cab. I don't know about the load in the UA Ox. I have the Fryette Power Load and it sounds fine, but I'd go with one of the Suhr offerings if I were to purchase another.
 

Governator

New Member
I agree with the OP that Axe Fx 3 amp/cab tones sound "far away" and somewhat 2D when played back through FRFRs.

However, the OP also preferred the Axe Fx 3 for recording. This implies that a real amp with real mics on a real cab would sound the same or worse on playback through FRFRs -- but I disagree. Certain "real setup" recordings have an obvious quality of sounding "forward", gritty and clear. Example at 3:30 to 6:30:

I've never been able to achieve such clarity and forwardness with the Axe Fx 3 in a recording context. Is the Axe Fx 3 not quite capable (yet) of the real goods, or is it me?
 
Last edited:

Piing

Fractal Fanatic
For proper A/B comparison betwen the miked CAB and the Axe-Fx recordings, did you use a IR capture of the same CAB and Microphone at the same position?
 
Top Bottom